Devices intended to overcome the effects of phase intercept, notably the system described in U.S. Pat. No. 3,972,000, are known in the art. That system, which uses a phase-locked loop, effectively overcomes the effects of phase intercept under steadystate conditions, but is relatively slow to reach this state as are all phase-locked loop systems. It is, therefore, desirable to provide means for initializing the loop as quickly as possible before the data transmission starts.
Copending U.S. patent application Ser. No. 950,489 filed Oct. 11, 1978 by the present applicant describes a method for measuring the slope of the envelope delay characteristic of a transmission channel. The envelope delay characteristic represents the variations of the slope of the phase-frequency characteristic of the channel, and means have been found for deriving the phase intercept value from that of the slope of the envelope delay characteristic of the channel as measured in accordance with the method described in copending patent application Ser. No. 950,489.